More of P0600 - '[[nodiscard]] in the Library' mark empty() as nodiscard in string, string_view, and the free function std::empty(). Removed tabs from <string_view>, which is why the diff is so big.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@318328 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.capacity/empty.pass.cpp

@@ -9,17 +9,19 @@
 
 // <string>
 
-// bool empty() const;
+// bool empty() const noexcept;
 
 #include <string>
 #include <cassert>
 
+#include "test_macros.h"
 #include "min_allocator.h"
 
 template <class S>
 void
 test(const S& s)
 {
+    ASSERT_NOEXCEPT(s.empty());
     assert(s.empty() == (s.size() == 0));
 }